We wish to obtain a clearer understanding of the genetic basis of immunological functions controlled by the mouse MHC or H-2 complex through the analysis of its mutants. We will search for new mutations within the H-2 complex and in particular in the K, D, and I regions by skin grafting and serological techniques, and also for recessive lethal alleles (non-t-series) in Chromosome 17. We wish to study the genetic fine structure of the K and D regions in which numerous mutants are known and to define individual gene loci in those regions by modern genetic methods. Our studies will include functional analysis of the gene products of the mutants found.